Luxman L-85V Troubleshooting

[waryan]

I picked up a Luxman L-85V a few days ago that has an issue. I could visually see a burned resistor and a popped (new) cap. Hoping someone here could point me in the right direction for next steps.

Here's what I've done so far on the Left Channel PB-1037:

-Replace output transistors with MJ21193/94
-Replace R20/R21 with 82 Ohm 1 Watt resistors. R20 was visibly burned when I received the unit.
-Replace C01 / C03 / C11 / C12 (C11 was blown when I received the unit)

After replacing these parts, R20 burns immediately on power up. Below is a link to the service manual if anyone can point me down the signal path for what to tackle next, I would be very grateful. Thank you.

https://www.audioservicemanuals.com...n-l-85-v/2353367-luxman-l-85-v-service-manual

 

[ivandezande]

I picked up a Luxman L-85V a few days ago that has an issue. I could visually see a burned resistor and a popped (new) cap. Hoping someone here could point me in the right direction for next steps.

Here's what I've done so far on the Left Channel PB-1037:

-Replace output transistors with MJ21193/94
-Replace R20/R21 with 82 Ohm 1 Watt resistors. R20 was visibly burned when I received the unit.
-Replace C01 / C03 / C11 / C12 (C11 was blown when I received the unit)

After replacing these parts, R20 burns immediately on power up. Below is a link to the service manual if anyone can point me down the signal path for what to tackle next, I would be very grateful. Thank you.

https://www.audioservicemanuals.com...n-l-85-v/2353367-luxman-l-85-v-service-manual

Why did you replace the output transistors? Why didn't you test any other transistors?????

What's attached to R20? - Q509. Survey says it's most likely bad.
You'll need to replace Q510 as well.
Try MJE15030/31 or 32/33. If bias isn't dialing in, try KSA940/KSC2073.

You need to also replace the epoxy/blob diodes in there. Those will hurt the DC offset.
I would carefully replace every transistor on the amp board.
Also replace the trimmers with Bourns 3386H type. The bias trimmer could be toast.

 

[waryan]

Why did you replace the output transistors? Why didn't you test any other transistors?????

What's attached to R20? - Q509. Survey says it's most likely bad.
You'll need to replace Q510 as well.
Try MJE15030/31 or 32/33. If bias isn't dialing in, try KSA940/KSC2073.

You need to also replace the epoxy/blob diodes in there. Those will hurt the DC offset.
I would carefully replace every transistor on the amp board.
Also replace the trimmers with Bourns 3386H type. The bias trimmer could be toast.

Hi Ivan - the output transistors were measuring as shorted. I did test the MJE15030/31 on the board and they tested good. A tech recapped this unit recently and replaced a number of transistors as well.

I will test the rest of the transistors and replace the blob diodes as the next steps. Thank you for the input.

 

[ivandezande]

Hi Ivan - the output transistors were measuring as shorted. I did test the MJE15030/31 on the board and they tested good. A tech recapped this unit recently and replaced a number of transistors as well.

I will test the rest of the transistors and replace the blob diodes as the next steps. Thank you for the input.

All this would have been good to know. Also I would say the tech should take this back under warranty.
There's MJE in there already? I would replace anyways.

 

[waryan]

All this would have been good to know. Also I would say the tech should take this back under warranty.
There's MJE in there already? I would replace anyways.

The tech who did the work recently passed. The work was done just a few months ago. I found that there were incorrect capacitor values in a few places, which is why I replaced several caps.

I have new MJE's on hand that I can toss in pretty quickly. Thank you.

 

[ivandezande]

The tech who did the work recently passed. The work was done just a few months ago. I found that there were incorrect capacitor values in a few places, which is why I replaced several caps.

I have new MJE's on hand that I can toss in pretty quickly. Thank you.

Yikes. Sounds good, I'd be checking all the work then. Great model, but there's a lot to replace for reliability.

 

[waryan]

Yikes. Sounds good, I'd be checking all the work then. Great model, but there's a lot to replace for reliability.

Started digging in on this board again today by testing all transistors. Q06 actually has a physical crack through the middle of it and measures as a diode with my Atlas DCA75 Pro transistor tester. Several other transistors don't measure at all or are showing as voltage regulators / diodes. I have ordered replacements for ALL transistors on the amp boards, as you suggested, Ivan.

One other question. I hooked up my Atlas ESR70 Gold that I use to check capacitance and did a quick run against the large filter capacitors. One comes in ~15200uF and the other comes in close to 18000. I understand 20% of 15000 is 3000, so this would technically be in spec, but am wondering if this is something you would recommend replacing at this point. I mean, I'm generally never against replacing 50-60 year old electrolytics, but I also don't love replacing stuff that measures correctly either. Thank you.

 

[ivandezande]

Started digging in on this board again today by testing all transistors. Q06 actually has a physical crack through the middle of it and measures as a diode with my Atlas DCA75 Pro transistor tester. Several other transistors don't measure at all or are showing as voltage regulators / diodes. I have ordered replacements for ALL transistors on the amp boards, as you suggested, Ivan.

One other question. I hooked up my Atlas ESR70 Gold that I use to check capacitance and did a quick run against the large filter capacitors. One comes in ~15200uF and the other comes in close to 18000. I understand 20% of 15000 is 3000, so this would technically be in spec, but am wondering if this is something you would recommend replacing at this point. I mean, I'm generally never against replacing 50-60 year old electrolytics, but I also don't love replacing stuff that measures correctly either. Thank you.

Good. That should get you where you need to be.

Replace them. They're 50 years old and that little meter can't measure at voltage the things that matter. I think I just used some CDE 382 series in mine.

If the output transistors fried be sure to check/replace the emitter resistors too.

 

[waryan]

Well, back to square one. I've replaced all transistors as well as any capacitor that had an incorrect value. Cranked it back up and R20 burned immediately again. Any thoughts on where to look next? Thank you.

 

[ivandezande]

Well, back to square one. I've replaced all transistors as well as any capacitor that had an incorrect value. Cranked it back up and R20 burned immediately again. Any thoughts on where to look next? Thank you.

Why are there three bipolar caps on the board? Why did you use Nichicon FG instead of KL for a tantalum replacement? Why aren't the trimmers both replaced with Bourns 3386H series? Why aren't the emitter resistors replaced? Some of the transistors you installed look like they're a mile off the board. The board in general looks like it needs to go through the dishwasher. Can't tell what's going on, can't even read the numbers on the transistors. What a mess.

I want to see well-lit photos of both sides with a decent camera. And cleaner work. Then we can see what's happening.

Double check all your transistor installations. Ohm out every single resistor on the board. I had the exact same failure mode on mine and it was a resistor that died but didn't show physically.

 

[waryan]

I replaced the Nichicon FG (that's what was in place when I received the unit and didn't think twice about it). I replaced the other trimmer. I also replaced all resistors on the board except for the .33uf 5W resistors. I had to order some and will come back to this once they are in. Thank you for your help.

 

[waryan]

Hi Ivan - so, I replaced basically all components on the board and the resistor no longer burns! However, the fuse blows as soon as I give power. Any thoughts on next steps?

I did replace the filter caps, to no avail. The 4 big diodes on PB-1038 test good. If I crank it up without the amp boards connected, the relay clicks and it comes on. As soon as I connect one or the other amp boards (or both), the fuse goes. I’ve cleaned connections up the best I can to ensure there is not a simple short.

I do have a new transistor coming for Q05 - the parts list was incorrect. Thank you.